Despite the importance of employees in influencing plan choice, virtually nothing is known about how they choose the set of plans offered to employees. Employer decisions regarding health plan offerings are important to policy makers because restrictions on plan choice by employers could have important consequences for the care received by their employees. This proposal will investigate the determinants of employer decisions regarding which health plans to offer with an emphasis on the relationship between employer selection of health plan and plan performance. Because commonly used performance measures are limited employer selection of health and plan performance. Because commonly used performance measures are limited to HMOs, the project will focus on that decisions regarding which HMOs to offer. The project makes use of a unique dataset provided by MEDSTAT that identifies the health plan choices of over 60 large employers operating in over 288 MSAs in which there are competing HMOs. By focusing on large employers, this work will explore the segment of market most likely to be responsive to plan performance. We will father data over a four year period allowing us not only to access the cross sectional relationship between employer plan choice and performance, but allow to track over time whether the salience of performance measure change and if performance influence changes in plan offerings. The analysis will also control for plan premiums and the breadth of plan provider networks, allowing us to identify the importance of those traits relative to plan performance.